In the following description and the accompanying claims, the expression “closure device” will be used to generally indicate any element movable between an open position and a closed position, respectively opening and closing an access to an inner compartment of a motor vehicle, therefore including, boot, rear hatches, bonnet lid or other closed compartments, window regulators, sunroofs, in addition to the side doors of a motor vehicle, to which the following description will make explicit reference, purely by way of example.
It is known that electrical latches are provided in motor vehicles, for example for controlling opening and closing of the side doors.
An electrical door latch generally includes a ratchet that is selectively rotatable with respect to a striker fixed to a door post, in order to latch and unlatch the door. The electrical door latch includes a pawl that selectively engages the ratchet to prevent the ratchet from rotating. The electrical door latch includes an electric motor, which is electrically connected to a main electric power supply of the vehicle (for example to the 12V battery of the same vehicle), in order to directly or indirectly drive the pawl, via an electrically-operated actuator.
As it is known, a common problem related to electrical latches is that of controlling, as it is also required by security regulations, opening and closing of the doors even in case of failure of the main power supply of the vehicle, or in case of interruptions or breaking of the electrical connection between the main power supply and the electric motor in the latch; this kind of situation may occur for example in case of an accident or crash involving the vehicle.
A possible solution to this problem envisages the use of a mechanical release mechanism in the latch, which serves as a manual backup to the electrically activated side door latch.
However, the presence of a redundant mechanical mechanism entails higher area occupation and weight and additional costs, and also represents a further constriction for designing the door.
Therefore, the use of a backup power source for the electrical latch has been proposed, in order to supply electrical energy to the electric motor of the latch, in case of failure or interruption of the vehicle main power supply.
This backup power source is usually kept in a charged state during normal operation, by the main power supply, so as to be readily available as soon as the need arises, for example in case of a crash or accident.
However, designing of a backup power source, and of the related electronic circuitry, for the electric latch assembly has proven to be a difficult task, for example due to size requirements, as also has proven to be difficult meeting desired electrical performance, for example in terms of energy density or current output, especially in automotive operating conditions.
In this respect, EP 0 694 664 A1 discloses a backup energy source for a door latch, designed to supply power to the latch during emergency situations, which envisages an auxiliary battery arranged within the door where the latch is placed.
Another known solution, discussed in DE 201 21 915 U1, discloses the use of a capacitor group as a backup power source for a vehicle door latch. The capacitor group is coupled to a circuit board, externally connected to the latch assembly. The capacitor group includes a vast number of capacitors, of the high voltage type (withstanding up to V), series or parallel connected, thus requiring a relevant amount of space on the circuit board; moreover, such solution generally needs a further backup energy source, since the supercapacitor group may only be able to supply power for a limited amount of time. In other words, the capacitor group may not be able to guarantee a sufficient and autonomous backup energy source for the vehicle latch.
A need is therefore felt in the field for an optimized and reliable backup power source for an electric latch in a motor vehicle.